> Road wear scales with the fourth power of weight over an axle.
Cars are not getting more axles, even SUVs, so this is a constant multiplicative factor. I would be happy with a tax that scales as the fourth power of the mass, no problem. That would be actually quite dissuasive very quickly. Though even a linear scaling would be an improvement over the current situation.
> Most fuel consumption is about overcoming drag rather than accelerating so you should expect it to scale with something like cross-sectional area, say weight^2/3, though making cars longer adds weight without much drag and making them boxier can add drag without much weight.
Right. We should ideally account for aerodynamics and drag factors, which also keep getting worse year after year. One does not preclude the other.
> I don’t think fuel taxes are particularly good as indirect taxes on the externalities one might care about
I entirely agree.